ARM: dts: imx51-zii-rdu1: Use preferred i2c-gpios properties

ARM: dts: imx51-zii-rdu1: Use preferred i2c-gpios properties

The 'gpios' property to describe the SDA and SCL GPIOs is considered
deprecated according to i2c-gpio.yaml.

Switch to the preferred 'sda-gpios' and 'scl-gpios' properties.

This fixes the following schema warnings:

imx51-zii-rdu1.dtb: i2c-gpio: 'sda-gpios' is a required property
	from schema $id: http://devicetree.org/schemas/i2c/i2c-gpio.yaml#
imx51-zii-rdu1.dtb: i2c-gpio: 'scl-gpios' is a required property
	from schema $id: http://devicetree.org/schemas/i2c/i2c-gpio.yaml#

Signed-off-by: Fabio Estevam <festevam@denx.de>
Signed-off-by: Shawn Guo <shawnguo@kernel.org>